The field of the disclosure relates generally to a motor controller for an electric motor and, more specifically, a motor controller that enables accurate airflow at low airflow output levels.
Electric motors are typically torque-calibrated when manufactured to ensure the torque output at the drive shaft of the electric motor matches the torque commanded. At least some electric motors, particularly electric motors driving blowers, are further calibrated to produce a constant airflow during operation in either a torque-control mode or a speed-control mode. Such a calibration quantizes airflow output for a given speed and torque output when driving the blower. The actual airflow output can vary according to the blower construction, duct or other airflow restriction into which the airflow is directed. Further, estimating airflow output for a given speed and torque is subject to numerous sources of error, including, for example, parasitic current and noise in current sensing and current regulation circuits, magnetic flux changes with temperature, effects of magnetic flux on average current during peak current regulation, variability in bearing friction, variation and drift in calibration procedures and equipment, and imperfections in drive torque production linearity.
While estimations of airflow output remain accurate when operating over certain portions of the speed-torque operating profile, i.e., the calibration region where the above-mentioned sources of error are minimized, airflow output estimations generally exhibit greater error as airflow demand tends away from the calibration region. In particular, estimations of airflow output may exhibit significant error, e.g., up to plus-or-minus 10%, at low airflow output levels, e.g., at or below approximately 10% torque output. Generally, error increases as airflow tends toward zero. Operation of blowers at low airflow output levels is increasingly important to achieve efficiency targets.